feat(voice): SSE bridge + Siri-blob overlay for wake-word script

Adds the tablet side of voice assistant integration. External Python
script (openWakeWord + Groq STT + OpenClaw) will POST state transitions
to /api/voice/event with a bearer token, and the tablet shows a
fullscreen overlay with Siri-style animated blob + current agent +
recognized text / response text.

- lib/voice-bus.ts — in-process EventEmitter singleton, preserved
  across hot reloads via globalThis
- app/api/voice/event — POST, bearer-auth via VOICE_API_KEY env,
  validates event kind, broadcasts on voiceBus
- app/api/voice/stream — GET, SSE endpoint, per-connection listener
  with 15s keep-alive ping and abort-signal cleanup
- components/VoiceOverlay — full-screen overlay, 3-layer pulsing
  Siri blob, per-agent palette (cosmo indigo/violet, lusya pink/rose),
  auto-dismiss timeouts (wake=20s safety, response=6s, error=4s),
  auto-reconnect on SSE drop
- middleware bypasses /api/voice/event so the script does not need
  a user auth cookie
- VoiceOverlay mounted in HomePageInner outside tab routing so it
  appears on every view

app/api/voice/stream/route.ts

@@ -0,0 +1,50 @@
+export const dynamic = 'force-dynamic'
+export const runtime = 'nodejs'
+
+import { voiceBus, VoiceEventPayload } from '@/lib/voice-bus'
+
+export async function GET(req: Request) {
+  const encoder = new TextEncoder()
+
+  const stream = new ReadableStream({
+    start(controller) {
+      let closed = false
+      const safeEnqueue = (chunk: string) => {
+        if (closed) return
+        try { controller.enqueue(encoder.encode(chunk)) } catch { closed = true }
+      }
+
+      // Initial hello — so client sees stream is alive
+      safeEnqueue(`: connected ${new Date().toISOString()}\n\n`)
+
+      const onEvent = (evt: VoiceEventPayload) => {
+        safeEnqueue(`data: ${JSON.stringify(evt)}\n\n`)
+      }
+      voiceBus.on('voice', onEvent)
+
+      // Keep-alive ping every 15s so proxies/browsers don't drop the connection
+      const pingTimer = setInterval(() => {
+        safeEnqueue(`: ping\n\n`)
+      }, 15000)
+
+      const abort = () => {
+        if (closed) return
+        closed = true
+        voiceBus.off('voice', onEvent)
+        clearInterval(pingTimer)
+        try { controller.close() } catch {}
+      }
+
+      req.signal.addEventListener('abort', abort)
+    },
+  })
+
+  return new Response(stream, {
+    headers: {
+      'Content-Type': 'text/event-stream; charset=utf-8',
+      'Cache-Control': 'no-cache, no-transform',
+      'Connection': 'keep-alive',
+      'X-Accel-Buffering': 'no',
+    },
+  })
+}